Blender 2.8 Eevee transparent BSDF leaving extruded text unfaced
To get a transparent material in EVEE we need to set the materials blend mode to alpha blend. When this is enabled the same time as show backface, the alpha of each face gets multiplied and makes the backfaces appear more prominent.

You need to turn off Show Backfaces in the material settings.



You also get a similar result with show backfaces when the blend mode is set to additive.